Bridge assemblies for variable resistors



March 11, 1958 G. A. RALSTON 2,826,664

BRIDGE ASSEMBLIES FOR VARIABLE RESISTOR-S Filed March so, 1956 9 3L 7 'Fig.l

INVENTOR.

Gavin A. Ralsfon wwm AGENT.

United States Patent 2,826,664 patented Mar. 11, 1958 2,826,664 BRIDGE ASSEMBLIES FOR VARIABLE RESISTOR S Gavin A. Ra'lston, Northport, N. Y., assignor to Micro Machine Works, Inc., a corporation of New York Application March 30,1956, SerialN 573,010 9Claims. (CI. mil-48) IlEhis invention :relates generally -'to variable resistor units, rheostats, potentiometers or the like and more specifically to bridges and bridge assemblies as are applied to tihe :Iesistance winding there for.

=In1tlrerommonrheostatsuch-as may be 'found in radios 'or intensity varyingelectric light controls, the resistance =coil.+contact arm normally travels less than 360 from aILDW ttva High position. This typ'ewof an installation iha's- 'stops -lo'cated at the desired points to limit the trav'el or movement of the contact arm -on the coil from the minimum to th s maximum positions.

lnithe mor-e complex servo-mechanisms, these variable resistors, potentiometers, in many installations are designed no=have the'conta'ct rotor rotate a full 366 even ithough the effective =arcua'te working range may be approximately 346. In'theseinstallations, the resistance coil-is made of afine=resistancc wire winding on 'a nonconductive core *or windingcard. Thiscore -or 'cardmay be originally of :a circular "form "or merely a fiat card which when wound -with the wire is formed in a circle as it is-installed in its mounting. The resistance coil is waniished,"balred and butfed, and, when installed 'in an-instrument with unlimited travel, the space or breach between the ends of 'the winding must he filled or have .a bridge applied *thereto to prevent the contact on the contact arm from snagging the end of the coil winding and dealing it away from the core. While these types of lillersand mechanical bridges are not new, they lack a most important added feature, that of providing a mechanical bondfor the coil ends. In addition, this new bridge installation has utility as a spacer for the terminal taps or tap contacts of the type disclosed in the pending United States patent application Serial Number 560,729 which was filed on January 23, 195 6, and assigned to a common assignee. While this type of a bridge "installation forms a mechanical bond and a,protector for the coil winding ends as well as acting as a spacer for the terminal taps or tap contacts, this bridge installation also provides a common passageway for the lead wires which connect the terminals to the various taps or tap contacts.

Therefore, it is an object of this invention to provide a mechanical bridge for resistance coils in variable resis-'tance units which forms a positive mechanical bond and a protector for the resistance coil ends, provides a spacer for the terminal taps or tap contacts and a common passageway through the coil winding card 'for the passage of the lead wires which connect the external terminals to the flaps or tap contact within the variable resistance unit.

These and other objects and advantages will become more apparent by reference to the following description and the accompanying drawing wherein:

Figure .1 is a plan view of a variable resistor 01' pctentiometer with the rotor element removed and incorporating the present invention;

Figure 2 is an enlargement of that portion of Figure 2 lwhich is enclosed within thecircular line 2 with the housing or case of the potentiometer removed;

Figure 3 is an'el'evational view of the present invention takenon lin'e-3-3 of-Figure-Z; and,

Figure 4 isa sectional view of the present invention taken on line 4"4 of Figure 3.

Now rferringmo the drawings, the preferred form of a variable resis'tor is shown as a potentiometer which has a cylindrical sh'll or case 10 which is normally metallic and fined thereto is a terminal board 12 which mounts the terminals 14, only two of which are shown.

Terminals- 14 are electrically connected to a -'commutato'r (not 'shown) and the various taps, tap contacts or terminal taps-a6 by the lead wires 48. Lining the shell 10 is-aninsulation 16, in this instance, being comprised of a synthetic, non-conductive ring or coil form 18 and a flanged, cup shaped member or tap disc 22. this fap dis'c-also being made of a non-conductive synthetic. Thisinsulation I6, lining the shell 10, not only segregates the electrical components within the potentiometer but is also the mounting structure for the taps, 'tapconta'cts or termln'al contacts 46 in a manner as is disclosed in the 'previously mentioned pending application. This insulation-additionally mounts the resistance coil #1 and a commutator '(not shown). When a syn- =theticmaterialis -used, the'two piece construction'of the insulation 16 is preferred-inasmuch as closer tolerances can be held to a greater degree than if the insulating meniber were formed'of a'singleunit. It should be'understood, that 'while this "is merely a preferred form, it does notp'reclu'dethe use of a single unit construction o'f t'he insulating menibe'r I6. The tap disc 22has a hub portion 24 which surrounds an enlarged portion (as is indicated by 'the inner "broken line circle in Figure l) o'f-the case or the shell T0 whichrnountsa rotor assembly (not shown) and is spaced therefrom to provide a circular passageway for the lead wires '48. Although the path of =the lead wires is not critical, these wires are preferably "coursed through the provided passageway within the hub portion 24 instead of around'the outside of the hub to prevent fouling on the taps and as an added precaution against shorting. There is a slot 30 in the flanged portion 28 of the tap disc 22 which extends through the base of the wall of the hub portion 24 of the tap disc 22 to provide an access for the lead Wires 48 to permit their entrance into the circular passa'g'eway within the 'hub where the lead wires attach to the individual tap contacts. This slot 30, upon assembly of the component parts of the potentiometer, is aligned with a tubular rivet or hollow fastener 42 which joins the coil form '18 of the insulation 16, the wire resistance coil '41 and the bridge 32.

This mechanical joint formed of the coil form 18, the resistance coil 41 and the bridge 32 all being held by the fastener 42 may be more clearly seen by referring to Figures 3 and 4 of the drawings. The coil form 18 has a hole 20 therethrough which has an enlarged mouth portion to receive the head of the fastener 42. The resistance coil '41 is formed of a non-conductive winding core or card 41C upon which is wound the resistance wire 41W. The resistance coil 41 may be prepared in any of the known andaccepted methods. Some of these may be found in volume 17 of the Radiation Laboratory Series," 1st edition, 3rd impression, 1949, entitled Components Handbook," which was edited by J. F. Blackburn and published by the McGraw-Hill Book Co., Inc.; chapter 8 which is entitled Potentiometers, by -F. E. Dole, pages 243 to 252, and which embraces section 8.1, The Resistance Element." In using a fiat card or a split ring type core for the winding, the ends of the card may be grooved to form an opening similar to the opening in the coil form, or, the card ends may be spaced from each other when the resistance coil 41 is inserted into the coil form 18, the full slot being comparable to the grooved opening. In using a full ring card, a hole must be cut or drilled which will permit the passage of the fastener 42. In using any of the card forms, the ends of the wire coil must be spaced from each other and from the opening for the fastener to prevent contact of these metallic parts. An alternate material for the fastener may be a non-conductive which would thus lessen the possibility of shorting in this area, but this material would additionally have to have sufficient strength and stability to maintain the joint under all conditions.

The bridge 32 is made of a non-conductive synthetic having a limited and predetermined degree of flexibility and has an opening 34 through which passes the fastener 42. The top surface 36 of the bridge 32 is generally flat and at a level, when the bridge is joined to the coil 41, slightly above the top of the coil and sloping downwardly as at 38 to a level, at the ends of the bridge, which is below the top of the coil, or, this top surface may be arcuate, the ends being below the top of the coil while that portion coextensive with the breach between the coil ends is above that level. The ends 40 of the bridge 32 are precut and when the component parts including the bridge are assembled, the bridge will extend a predetermined arcuate length about the center of the potentiometer, being coextensive with the breach between the coil ends and overlapping the said ends. The wire coil 41W extends beyond the ends of the bridge 32 and when the fastener 42 is upset or tightened, the center of the bridge is drawn against the coil card 41C, the ends of the bridge clamping the wire coil ends against the coil form 18 and thus forming a mechanical, clamp type bond on the wire 41W.

The fastener-42 may be of any of the hollow or tubular types, the central axial opening 44 forming a passageway through the bridge assembly which is comprised of the coil form 18, the resistance coil 41 and the bridge 32 and is aligned with the slot 30 in the tap disc 22. As can now be seen, the lead wires 48 which are joined to the terminals 14 within the terminal board 12 pass through an opening in the shell or case 10, then will traverse the passageway 44 inthe fastener 42, thence through the slot 30 in the tap disc 22, as previously described, to be finally joined to the taps, tap contacts or terminal taps 46.

The taps, tap contacts or terminal contacts 46 may be locked in place by the application of a homogeneous adhesive as described in the aforementioned pending application or by any of the other known and accepted methods. However, the terminal taps having a fixed gage for alignment, by the use of this type of a bridge installation, may merely be brought into abutment with the ends 40 of the bridge and in addition to being capable of being locked in place in the same manner as the other intermediate taps, may be locked to the bridge, instead of the tap disc or the resistance coil, with a similar adhesive.

A spring arm 52 of the potentiometer rotor (not shown) carries a contact 50 which electrically engages the top of the resistance coil 41. As the rotor turns, the contact 50 rides on the top of the winding until it meets one of the rising surfaces 38 of the bridge 32, thereupon, being carried upwardly to the top surface 36 of the bridge where, at that point, it is out of contact with the resistance coil 41, as is shown in Figure 4. The contact 50 is thus lifted off the resistance coil 41 and rides on the surface 36 of the bridge 32 until it passes across the breach between the ends of the wire coil and then returns to an electrical contact with the coil as it travels down the second sloped surface 38.

A modified form of the bridge 32, which is not shown in the drawings, would have elevated top surfaces which would form stops at the ends of the bridge. This type of a bridge would be used in rheostats where the contact travels from a minimum position to a maximum position on the resistance coil. This type of a bridge assembly would also provide a mechanical type bond for the wire coil ends, a common passageway for the lead wires and also act as a spacer for the terminal contacts.

As can now be seen, the bridge normally not only carries the rotor contact over the breach between the ends of the wire coil, but also spaces the terminal taps or tap contacts while the hollow fastener provides a common passageway for all the lead wires into the instrument. In addition, by drilling the head off the fastener, the resistance coil bridge assembly may be disassembled easily to facilitate the replacement of any of the component parts that may be or become defective.

Having thus described my invention in the preferred form, I claim:

1. In a variable resistor having a contact rotor assembly associated therewith, the combination comprising a substantially cylindrically-shaped insulation housing provided with an inner peripheral flange portion, a resistance element comprising a resistance wire wound on a flexible linear non-conductive core member which is contoured and positioned around the inner peripheral flange portion of said cylindrical housing with the ends thereof spaced from each other, a non-conductive resilient bridge member mounted in overlying relationship to the ends of said contoured linear resistance element and secured to said housing such as to clamp said ends firmly against the peripheral flange portion thereof, said bridge member being formed with a raised center portion extending above the top edge of said resistance element and being sloped downwardly at each end to a level below the top edge of said resistance element, thereby defining an insulated supporting track for carrying a rotor contact across the break between the ends of said resistance element, and a pair of conductor leads and contact taps electrically connecting-the ends of said resistance element to terminal points provided externally of said cylindrical housing.

2. In a variable resistor having a contact rotor assembly associated therewith, a substantially cylindrically-shaped insulation housing provided with an inner peripheral flange portion, a resistance element comprising a resistance element comprising a resistance wire wound on a flaxible linear non-conductive core which is contoured and positioned around the inner peripheral flange portion of said cylindrical housing with the ends thereof spaced from each other, a non-conductive resilient bridge member mounted in overlying relationship to the ends of said contoured linear resistance element, a hollow fastener extending through said housing and bridge member securely clamping the ends of said resistance element against said flange, a pair of resilient contact members mounted in electrical contact with said resistance element and spaced from each other by means of said bridge member, a pair of insulated lead wires joined each to one of said contact members and extending through said hollow fastener to the exterior of said housing, the top edge of said bridge member extending above the top edge of said resistance element and the ends thereof being sloped downwardly to a level below the top edge of said resistance element and forming a rotor contact supporting track for raising the contact off the resistance element and permitting the same to traverse the breach between the ends of said resistance element out of contact with the same.

3. In a variable resistor having a contact rotor assembly associated therewith, a substantially cylindricallyshaped insulation housing provided with an inner peripheral flange portion, a resistance element comprising a re sistance wire wound on a flexible linear non-conductive core which is contoured and positioned around the inner peripheral flange portion of said cylindrical housing with theends-thereof-spaced from-eacluotherganon-conductive aresilient bridge member -mounted in overlying xelationship to the ends of said contouredfllinear-resistance element, a hollow fastener extending through said housing and bridgemembersecurely clampingttheendsof said resistance clement against said flange, a pair of resilient contact members mounted in-electrical-contact with said resistance ielement andspaced from-each other by means ofusai'd bridge member, .a pair of zinsulated tlead iwires zjoinedteach -'to one of ,said contact members and extend- :ing through .saidlhollow fastenento -,the exterior ofsaid housing, .the top edge of {said bridge-1membcr extending above the top edge of said resistance element with the end edges of said bridge member forming stop surfaces to prevent travel of a rotor contactor beyond the ends of said resistance element.

4. A multi-purpose bridge assembly for variable resistors having a contact rotor assembly associated therewith, comprising an insulated housing, a substantially cylindrical open-ended resistance element mounted within said housing, a non-conductive bridge member mounted within said housing in overlying relationship to the ends of said resistance element, a hollow fastener extending through said housing and bridge and serving to retain the bridge, resistance element and housing in fixed position with respect to each other, a pair of terminal contacts abutting the ends of said bridge and mounted in electri cal contact with the respective ends of said resistance element, a pair of terminal conductor leads secured one to each of said terminal contacts and extending to the exterior of said housing through said hollow fastener, the top edge of said bridge member extending above the top edge of said resistance element and the ends thereof being sloped downwardly to a level below the top edge of said resistance element to form an inclined rotor contact supporting track for raising the contact off the resistance element and permitting the same to traverse the gap between the ends of said resistance element out of contact with the same.

5. A multi-purpose bridge assembly for variable resistors having a contact rotor assembly associated therewith, comprising an insulated housing, a substantially cylindrical open-ended resistance element mounted within said housing, a non-conductive bridge member mounted within said housing in overlying relationship to the ends of said resistance element, a hollow fastener extending through said housing and bridge and serving to retain the bridge, resistance element and housing in fixed position with respect to each other, a pair of terminal contacts abutting the ends of said bridge and mounted in electrical contact with the respective ends of said resistance element, a pair of terminal conductor leads secured one to each of said terminal contacts and extending to the exterior of said housing through said hollow fastener, the top edge of said bridge member extending above the top edge of said resistance element with the end edges of said bridge member forming stop surfaces to prevent travel of a rotor contactor beyond the ends of said resistance element.

6. In a variable resistor having a case and a contact rotor assembly, a terminal board secured to the case having a plurality of terminals mounted thereon, an insulated liner mounted within said case and provided with a central hub portion and a peripheral flange portion, an open-ended electrical resistance element mounted within said insulated liner in contact with the peripheral flange portion thereof, a non-conductive bridge member mounted within said insulated liner against the open-ends of said resistance element and bridging the gap therebetween, fastener means clamping said bridge member into firm contact against the ends of said resistance element and securing the bridge and resistance element in a fixed position with respect to said insulated liner, a pair of contact taps positioned in electrical contact one with each of the ends of said resistance element and mounted within the hub ,portion of .said insulated 4liner, -insulated-- leadwires electrically connecting said rteuninalsrtoisaid contact-taps .through said fastener -means,.said-bridge member'being -.formed withaxaisedscenter portion extendingfabove the rotonassembly a -terminahboard secured to .the-case .hav-

ing a plurality of terminals mounted thereon, an insulated liner mounted within said case and provided with a central hub portion and a peripheral flange portion, an openended electrical resistance element mounted within said insulated liner in contact with the peripheral flange portion thereof, a non-conductive bridge member mounted within said insulated liner against the open-ends of said resistance element and bridging the gap therebetween, fastener means clamping said bridge member into firm contact against the ends of said resistance element and securing the bridge and resistance element in a fixed position with respect to said insulated liner, a pair of contact taps positioned in electrical contact one with each of the ends of said resistance element and mounted within the hub portion of said insulated liner, insulated lead wires electrically connecting said terminals to said contact taps through said fastener means, the top edge of said bridge member extending above the top edge of said resistance element with the end edges of said bridge member forming stop surfaces to prevent travel of a rotor contactor beyond the ends of said resistance element.

8. In a variable resistor having a case and-a contact rotor assembly, a terminal board provided with a plurality of terminals mounted on said case, an insulated liner disposed within said case and having a central hub portion and a peripheral flange portion, an electrical resistance element housed within the insulated liner in contact'with said flange portion; said resistance element having a breach between the ends of the electrically conductive portion thereof, a nonconductive resilient bridge substantially coextensive with said breach and overlapping the spaced ends thereof, terminal taps in electrical contact with said resistance element and mounted within the hub portion of said insulated liner, said terminal taps abutting the ends of the bridge and spaced apart thereby, a fastener member extending through the flange, the breach in said electrical resistance element, and the bridge member and joining and retaining these members in a fixed relationship, insulated conductor leads electrically coupling said taps to said terminals, a rotor assembly mounted within said case for rotation about the hub portion of said liner and including a contact wiper in electrical contact with said resistance element, the top surface of said bridge member extending above the top edge of said resistance element and the end portions of said bridge member being sloped downwardly to a level below the top edge of said resistance element, thereby forming an insulated track for the contact wiper permitting the same to traverse the breach between the ends of the resistance element while out of contact with the same.

9. In a variable resistor having a case and a contact rotor assembly, a terminal board provided with a plurality of terminals mounted on said case, an insulated liner disposed within said case and having a central hub portion and a peripheral flange portion, an electrical resistance element housed within the insulated liner in contact with said flange portion, said resistance element having a breach between the ends of the electrically conductive portion thereof, a non-conductive resilient bridge substantially coextensive with said breach and overlapping the spaced ends thereof, terminal taps in electrical contact with said resistance element and mounted within the hub portion of said insulated liner, said terminal taps abutfing the ends of the bridge and spaced apart thereby, a fastener member extending through the flange, the breach in said electrical resistance element, and the bridge member and joining and retaining these members in a fixed relationship, insulated conductor leads electrically coupling said taps to said terminals, a rotor assembly mounted within said case for rotation about the hub portion of said liner and including a contact wiper in electrical contact with said resistance element, the top edge of said bridge member extending above the top edge of said resistance element with the end edges of said bridge member forming stop surfaces to prevent travel of a rotor contactor beyond the ends of said resistance element.

References Cited in the file of this patent UNITED STATES PATENTS 1,381,093 Teegarden June 7,1921 2,007,462 Stoekle July 7, 1935 2,031,211 Dumke Feb. 18, 1936 2,676,226 Mneher Apr. 20, 1954 2,738,405 Iorgensen et a1. Mar. 13, 1956 U. 8-. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 2,826,664 March 11, 1958 Gavin'A. Bale-hon It is hereby certified of the above numbered patent requiring c Patent should read as corrected below.

that error appears in the printed specification orrection and that the said Let oers strike out "comprising a. resistance eleread --flexible-.

Column 4, lines 45 and 46 ment"; line 47, for "flexible Signed and sealed this 27th day of May 1958.

(SEAL) Atfieet:

KARL H. AXLINE Atteeting Officer ROBERT C WATSON Conminioner of Patents U. 3-. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,826,664 March 11, 1958 Gavin A. Ral ston' It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let uers Patent should read as corrected below.

Column 4, lines 45Jand 46, strike out "comprising a resistance element"; line 47, for "flexible" read --flexible--.

Signed and sealed this 27th day of May 1958.

(SEAL) Atteet:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Conminioner of Patents 

